During the 1980s, transportation planners and researchers emphasized the need for new technologies for solving the rapidly worsening problems of road transportation systems. This emphasis led to various research and development activities for new systems in the public sector, the automotive industry, and academia, which have generally been referred to as Intelligent Vehicle-Highway Systems (IVHS). J. G. Bender, "An overview of system studies of automated highway systems", IEEE Transactions on Vehicular Technology, Vol. 40, pp. 82-99 (1991).
One of the functional areas of research within the IVHS programs has been directed to Advanced Vehicle Control Systems (AVCS). AVCS represents a broad grouping of technologies and potential products, including concepts for systems that would take complete control of the movement of a vehicle, systems that would assist a driver in controlling a vehicle, and systems that would provide "high-bandwidth" information to a driver, particularly about imminent hazards. Automatic vehicle following systems, which would enable vehicles to automatically follow other vehicles at safe distances, have also been identified as an area of research in critical need for the development of practical and effective solutions.
Vehicle following, i.e., following another vehicle at a safe distance, is one of the most frequent driver tasks, and one which often causes driver fatigue and dozing. Driver fatigue in turn causes delays and errors in braking, passing, negotiating obstacles or curves, or recognizing signs and signals, resulting in an unavoidable toll of accidents and congestion. Indeed, it is believed that over 90% of traffic accidents are caused by such human errors. If driver and/or vehicle reaction time could be decreased by only 1 second, it is believed that over 80% of such accidents could be eliminated.
With increasing traffic volume, the traffic density increases, and the distance between vehicles correspondingly decreases, thus making vehicle following a more intense driving task. Vehicle following will therefore become an increasingly important focus for vehicle automation in order to reduce related traffic problems and accidents and increase efficiency. Accordingly, automatic vehicle following is believed to be a necessary function of any vehicle control system for successful transportation automation.
Previous research related to vehicle following technology varies in method and aspect, but generally falls within three categories: (1) fully autonomous systems based on vision, I. Masakii, Vision-Based Vehicle Guidance, New York, Springer-Verlag (1992); (2) systems based on roadway reference, Kehtarnavaz et al., "Visual control autonomous vehicle (BART)--vehicle following problem", IEEE Transactions on Vehicular Technology, Vol. 40, pp. 654-662 (1991); and (3) systems based on roadway guidance and central control, Shladover et al., "Automatic vehicle control developments in the PATH program", IEEE Transactions On Automatic Control, Vol. 40, No. 1, pp. 306-315 (1991).
In one vision-based system, a pair of stereo cameras were mounted on the front of a vehicle to measure the distance from a preceding vehicle, and to measure the heading angle of the preceding vehicle relative to the following vehicle. One advantage of this type of system is that it functions independently of either a central transportation system or a roadway guidance system. However, such a system is reliable only at relatively slow speeds. Also with this system the vehicle is controlled by following the preceding vehicle itself, as opposed to the path of the preceding vehicle, and therefore the following vehicle typically must remain sufficiently close to the preceding vehicle for the system to work reliably. Another drawback with the vision-based system is that it is sensitive to illumination conditions.
The systems based on roadway references, such as lines or marks on the road to guide the vehicle, are less complicated in terms of vehicle control in comparison to other systems. These types of systems control the vehicle to follow the roadway references, as opposed to the preceding vehicle or path of the preceding vehicle. The reliability of these systems are thus dependent on both environmental conditions and the condition of the roadway references. For example, construction on the roadway, or poor weather conditions, such as rain, snow or fog, can prevent the system from recognizing the lanes or other necessary references on the roadway.
In the central control systems, a following vehicle receives path information about a preceding vehicle from a central transportation control system. However, it is believed that the technology necessary for these types of systems will not be available in the near future.
Accordingly, it is an object of the present invention to overcome the drawbacks and disadvantages of other proposed vehicle following systems, and to provide such a system that enables vehicles to automatically follow each other at safe distances under various speed, roadway and weather conditions.